Laws of Nature

The discovery of the laws of nature has long been considered a principal aim of science. Of course, many laws that science discovers are not commonly designated “laws.” Alongside Boyle’s law, the law of universal gravitation, and the law of supply and demand, there are Archimedes’ principle, Maxwell’s equations, and the formulas of stoichiometry. Philosophy does not aim to account for the use of the term “law” or to discover the natural laws. Rather, philosophy strives to understand what it is that scientists discover when they discover laws. Philosophers have generally distinguished laws from “accidents” (that is, from contingent facts that are not matters of law) on several grounds. First, laws stand in especially intimate relations to subjunctive conditionals and counterfactual conditionals. Second, laws can explain why various facts hold. Third, laws help to give causes their powers to produce their effects. Fourth, laws restrict what is possible in nature; laws are universal and cannot be violated. (They possess “natural necessity.”) Fifth, laws specify the properties characteristic of various natural kinds. Sixth, when scientists confirm that some general hypothesis makes accurate predictions regarding each of the unexamined cases there might be, lying in a vast range, scientists are often basing their inductive reasoning on the presupposition that this hypothesis may be a law. Thus, laws are central to a wide range of core topics in metaphysics and epistemology. A philosophical account of natural law must refine these various respects in which laws are supposed to differ from accidents. It must then specify what laws are such that they are capable of playing their distinctive scientific roles. A wide variety of rival accounts of law has been proposed. Some philosophers defend “non-Humean” accounts, according to which laws are constituted by irreducible necessities, subjunctive facts, essences, or causal powers—or laws are themselves fundamental rather than reducible to other sorts of facts. Other philosophers defend “Humean” accounts, according to which the laws are reducible entirely to some non-modal features of the universe’s actual past, present, and future history, together perhaps with some features of scientists, their theories, or their practices. Yet other philosophers deny that the category of “laws of nature” is helpful for understanding science or reality. Some philosophers investigate the extent to which laws arise in the biological and social sciences. Although the nature of natural law was of great interest to early modern philosophers, this article is confined to works of analytic philosophy after 1945.